The objectives of our studies on mammalian spermatozoa are to investigate the unique architecture of the male gamete in chemical terms and to elucidate the relationship between spermatozoan structures and specialized functions. We have recently devised methods for quantitatively separating spermatozoan heads from tails using proteolytic enzymes and for completely removing midpiece organelles from the underlying axoneme filaments. We are using these methods, in combination with techniques for specifically labelling the DNA, the surface membrane, and the acrosomal membrane, to isolate heads, tails, and midpiece material from mammalian spermatozoa. These structures are being subjected to detailed chemical, cytochemical and ultrastructural analyses in order to localize important enzymes and proteins on the structures, to isolate these macromolecules and to define their roles in the various functions of the gamete. We expect that the results of these investigations will have important implications for understanding and controlling fertility.